1. Field of the Invention
The present invention relates in general to an acoustic transducer and pertains, more particularly, to a flextensional polygon transducer which, inter alia, provides large displacements at low acoustic frequencies.
2. Background Discussion
A number of so-called flextensional transducer designs have evolved based on the patents of W. J. Toulis, U.S. Pat. No. 3,277,433, "Flexural-Extensional Electromechanical Transducer", Oct. 4, 1966 and H. C. Merchant, U.S. Pat. No. 3,258,738, "Underwater Transducer Apparatus", June 28, 1966. In the invention of Toulis an oval-shaped cylindrical shell is driven along its major axis by a stack of piezoelectric bars resulting in a magnified motion of the shell in the minor axis as driven by the piezoelectric stack. The motions are opposite in phase the major to minor axis if the shell is in the shape of an ellipse. In the H. C. Merchant invention the shell is curved inward in a concave way so that the motion along the major axis and the ends is in phase with the motion in the direction of the minor axis.
These prior art patents are limited to a transduction in which four orthogonal surfaces are in motion. In one case all four move in phase while in the other case the orthogonal motions are out of phase. In neither case are the directions of major motion in the same direction as the motion of the transduction mechanism. In both of these prior patents the direction of the magnified motion is in a direction which is orthoqonal to the driver direction. Moreover, only two major surfaces produce the large motion which may result in directional acoustic radiation at frequencies higher than the fundamental shell system resonance. Also, since the driver mechanism is very stiff compared to the shell the resonance of the driver is much higher than that of the shell making it difficult to design the system with a coupled resonance. In the case of the above two patents the driver stack is operated as a stiff spring attached to the two ends of the shell along the major axis. On the other hand the invention disclosed herein overcomes these limitations and adds a new degree of motion which is in the same general direction as the shell motion.